1. Field of the Invention
The invention relates in general to elevator systems, and more specifically to new and improved methods and apparatus for improving the timely interchange of mode (command) and status information between a plurality of elevator cars and a dispatcher processor.
2. Description of the Prior Art
Elevator systems, having a plurality of elevator cars under group supervisory control by a dispatcher function, may utilize a digital computer in the implementation of the dispatcher function. U.S. Pat. No. 3,804,209, which is assigned to the same assignee as the present application, discloses a dispatcher which utilizes a digital computer, with a computer-aided dispatcher function hereinafter being referred to as a dispatcher processor (DP). Suitable operating strategy for the DP is disclosed in U.S. Pat. No. 3,851,733. Individual car control suitable for operating alone, or under group control by a DP, is disclosed in U.S. Pat. No. 3,750,850. These patents, all of which are assigned to the same assignee as the present application, are hereby incorporated by reference, and will be hereinafter referred to as the incorporated patents.
The incorporated patents describe an elevator system in which the DP controls each elevator car via a separate high speed serial data link, and the DP reads the status of each eleveator car via another separate high speed data link. While this is a completely satisfactory arrangement, it does require a computer having a fast cycle time, and having substantial memory, such as a minicomputer.
With the relatively low cost microprocessor now available, it is attractive to use it to construct a still relatively low cost microcomputer, and to use a plurality of microcomputers to perform the tasks formerly provided by electromagnetic relays and/or hard wired logic. This arrangement can greatly reduce the burden placed on the DP, enabling its function to also be provided by a microcomputer. However, a plurality of microcomputers must work together in harmony, without inefficiency or lost time, as it is critical that the car status information prepared by the elevator cars and sent to the DP, relative to their current operating status, be timely, so that the DP strategy is always applied to the situation as it presently exists. Otherwise, the DP signals to the elevator cars which control their operating modes will not be timely, causing inefficiency and poor elevator service to the building. Also, even if the mode control signals prepared by the DP are prepared with the use of timely car status information, these car mode signals must be promptly sent to and received by the elevator cars, or the status of the elevator cars may change appreciably by the time they receive the car mode signals, again causing inefficiency and degraded elevator service.